The invention relates to a screw clamp having a fixed bracket with a clamping surface, and having a sliding bracket which can be displaced and secured on a slide rail, the rail being connected to the fixed bracket, and the sliding bracket being carrier for a threaded spindle with a rotatably mounted clamping plate at its end.
Various embodiments of such screw clamps are known. For example, so-called all-steel screw clamps are commercially available, in which the fixed bracket and the slide rail are made integrally, for example from cold-drawn steel. Also known are screw clamps in which a fixed bracket made, for example, from malleable cast iron, is arranged fixedly on a steel slide rail. A sliding bracket produced, for example, from malleable cast iron can be displaced on the steel slide rail. In the case of the known screw clamps, the sliding bracket is braced, when a workpiece is clamped in, such that it is secured on the slide rail. Furthermore, in this case, various auxiliary means are known for the purpose of forming an antislip device. For example, DE-A1 32 18 486 may be mentioned in this context. This document contains an antislip device in the region of the through-passage between slide rail and sliding bracket. This device takes effect as soon as a workpiece is clamped in between the clamping plate and the fixed bracket. However, it has turned out, in particular in the case of all-steel screw clamps, that, despite the abovementioned antislip device, these screw clamps tend to loosen in the presence of vibration.